COMMENSURATE-INCOMMENSURATE TRANSITIONS IN MAGNETIC-BUBBLE ARRAYS WITH PERIODIC LINE PINNING

We report direct observations of commensurate-incommensurate phase tra nsitions as a function of bubble concentration in a two-dimensional ma gnetic bubble array subject to periodic line pinning. The pinning line s consist of lithographically produced parallel permalloy bars. Temper ature is simulated by an ac magnetic field. The structure function sho ws a smooth migration of Bragg peaks with density indicating a second order (or weakly first order) commensurate-incommensurate-commensurate transition as the local orientation of the array rotates continuously . We have also identified a commensurate smectic phase.